INSECT LIFE xvm
instantly there. Whichever is at the most favour-
able point drops upon the vanishing prey, and the
thing is done—the egg is laid.
There is ample evidence that the Bembex is
conscious of danger, and knows how disastrous for
the future of her nest is the presence of the hated
fly; her long- efforts to throw the parasites off her
track, her hesitation and flights, leave not a doubt on
the subject. How is it then, I ask myself once
more, that the enemy of Diptera should allow herself
to be annoyed by another Dipteron—a tiny robber,
incapable of the least resistance, which, if she chose,
she could destroy instantly ? Why, when once free
from the prey which hampers her, does she not
pounce on these ill-doers ? What is needed to ex-
terminate the evil brood around her burrow ? Merely
a battle which would take but a few instants. But
the Harmony of those laws which govern the preser-
vation of species will not have it so, and the Bembex
will always allow herself to be harassed without ever
learning from the famous "struggle for life" the
radical means of extermination. I have seen some
which, pressed too closely, let fall their prey and
flew off wildly, but without any hostile demonstra-
tion, although dropping their game left them full
liberty of action. The prey, so ardently desired a
moment earlier by the Tachinidae, lay on the ground
at the mercy of them all, and not one cared about it.
It had no value for the flies, whose larvae need the
shelter of a burrow. It was valueless also to the
Bembex, who came back, felt it for an instant and
left it disdainfully. The little break in her custody
of it had rendered her suspicious of it